• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.749-752
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• 2005

When an electric field higher than a characteristic coercive field is applied to a ferroelectric such as $LiNbO_3$, the orientation of the spontaneous polarization is reversed, which causes the reversal of the sign of odd-rank tensor properties such as electro-optic and nonlinear optic coefficients. A fabrication process of insulator and periodic external field assisted poling of a z-cut $LiNbO_3$ have been optimized for a periodic $180^{\circ}$ phase inversion along z-axis. The poling jig and the poling control system, fully controlled by a computer, for high quality and reproducible PPLN fabrication have been devised. Periodically polarization reversed PPLN was adjusted based on the fabricated thickness of insulator. The poling structure of PPLN was observed under a microscope after etching PPLN samples by an etching solution ($HF:HNO_3$ = 1 : 2) for about 15 min.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2015.10a
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• pp.397-400
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• 2015

In this paper a solar energy harvesting system with low-cost MPPT control for low duty-cycled sensor nodes is proposed. The targeted applications are environment, structure monitoring sensor nodes that are not required successively to operate, and MPPT(Maximum Power point Tracking) control using simple circuits is low-cost differently than existing MPPT control. The proposed MPPT control is implemented using linear relationship between the open-circuit voltage of a solar cell. The designed MPPT circuit traces the maximum power point by sampling periodically the open circuit voltage of the solar cell and delivers the maximum available power to the load. The proposed circuit is designed in 0.35um CMOS process. The designed chip area is $975um{\times}1025um$ including pads. Measured results show that the designed system can track the MPP voltage by sampling periodically the open circuit voltage of solar cell.

• International Journal of Fluid Machinery and Systems
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• v.6 no.2
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• pp.87-93
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• 2013

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.

• The Korean Journal of Ecology
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• v.22 no.2
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• pp.69-77
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• 1999

Secondary vegetation. the holistically integrated system of nature and human being, is the complicated ecosystem that is composed of natural and man-created factors. Understanding the ecological function of secondary vegetation supplies us many important informations for sustainable landscape management and ecological restoration planning. In this research, we tried to examine the shape effect of vegetation patch on early structure of populations of pine and oaks. Moreover. we also tried to clarify the ecological functions of patch edge by exploring the patch effect on germination using patch index. In addition, we present the landscape structure of man -made vegetation of our study area, and setting experimental design of research. Vegetation landscape of study area is typical human disturbed landscape mainly composed of disturbance patches. Vegetation types of graveyard and managed pine forest were controlled by periodically repeated management. However, current seedlings of pine occurred well at both vegetation types. Presence of both saplings were more controlled in managed pine forest (PDM) and graveyard (G) than those of undergrowth (PD) and forest edge (FE) with canopy trees. The number of pine seedlings increased with patch size and patch perimeter. That of oak seedlings was, however, not significantly different. Larger graveyards provided higher light availability for germination of pine seedlings. We think, however, most seedlings of both species in the large sized graveyards without shade will die more easily than that of small sized ones before rainy summer. Relationships between patch shape and germination of two woody species cannot be exactly explained enough yet in these results. More informations on spatial interaction of the total species with differently sized patches are necessary to solve the concept of patch effect on species colonization.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.957-962
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• 2012

Fluid/structure interaction (FSI) analysis is necessary to predict the response of a system in which aerodynamic pressure causes deformation of the structure, and vice versa. In dealing with a nonlinear behavior of the structure, however, a simple iterative algorithm of aerodynamic analysis with structural analysis yields no accurate results since aerodynamic pressure need to be changed in accordance with the deformation of structures. In this study, we explore an efficient and accurate method for integrating FSI analysis into structural nonlinear systems. During the course of nonlinear structural analysis, loading conditions are periodically updated by aerodynamic analysis. The accuracy and efficiency of the method is demonstrated with a high-aspect-ratio flexible wing of Global Hawk.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.325-331
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• 2010

In this study, highly miniaturized short-wavelength meander line employing eriodically patterned ground structure (PPGS) was developed for application to miniaturized on-chip passive component on GaAs MMIC (monolithic microwave integrated circuit). The meander line employing PPGS showed shorter wavelength and slow-wave characteristic compared with conventional meander line. The wavelength of the meander line employing PPGS structure was 17 % of the conventional meander line on GaAs MMIC. Due to its slow-wave structure, the meander line employing PPGS exhibited large propagation constant than conventional meander line, which resulted in larger phase shift and shunt inductance value. Above results indicate that the meander line employing PPGS is a promising candidate for application to a development of miniaturized on-chip RF components as well as inductor with a high inductance value on GaAs MMIC.

• International Journal of Contents
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• v.10 no.3
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• pp.84-89
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• 2014

The mass-spring model has been typically employed in physical-based simulators for clothes or patches. The mass-spring model frequently utilizes equal mass and the gravity factor. The model structure of masses supports a shape applicable to fishing nets. Therefore, to create a simulation model of a fishing net, we consider the mass-spring model and adopt the tidal-current and buoyancy effects in underwater environments. These additional factors lead to a more realistic visualization of fishing-net simulations. In this paper, we propose a new mass-spring model for a fishing-net and a method to simplify the calculation equations for a real-time simulation of a fishing-net model. Our 3D mass-spring model presents a mesh-structure similar to a typical mass-spring model except that each intersection point can have different masses. The motion of each mass is calculated periodically considering additional dynamics. To reduce the calculation time, we attempt to simplify the mathematical equations that include the effect of the tidal-current and buoyancy. Through this research, we expect to achieve a real-time and realistic simulation for the fishing net.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.463-470
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• 2008

Turbulent coherent structures near rod-roughened wall are investigated by analyzing the database of direct numerical simulation of turbulent boundary layer. The surface roughness rods with the height $k/{\delta}=0.05$ are arranged periodically in $Re_{\delta}=9000$. The roughness sublayer is defined as two-point correlations are not independent of streamwise locations around roughness. The roughness sublayer based on the two-point spatial correlation is different from that given by one-point statistics. Quadrant analysis and probability-weighted Reynolds shear stress indicate that turbulent structures are not affected by surface roughness above the roughness sublayer defined by the spatial correlations. The conditionally-averaged flow fields associated with Reynolds shear stress producing Q2/Q4 events show that though turbulent vortices are affected in the roughness sublayer, these are very similar at different streamwise locations above the roughness sublayer. The Reynolds stress producing turbulent vortices in the log layer ($y/{\delta}=0.15$)have almost the same geometrical shape as those in the smooth wall-bounded turbulent flows. This suggests that the mechanism by which the Reynolds stress is produced in the log layer has not been significantly affected by the present surface roughness.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.877-880
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• 2017

Impeller blades in the centrifugal compressor are subjected to static loads due to the high-speed rotation and steady aerodynamic forces. At the same time, aerodynamic excitations by the interaction between the impeller and the diffuser vanes(DV) periodically excite the impeller blades in resonant conditions, which may lead to high cycle fatigue (HCF) and eventually result in failure of the blades. In order to predict the structural response accurately, the aerodynamic excitation and the major resonant conditions were predicted by performing the unsteady flow analysis and modal analysis using ANSYS. Next, a unidirectional forced vibration analysis was performed by using fluid-structure interaction (FSI) method, and the safety of HCF was evaluated based on the results.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1330-1332
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• 2006

In the Langmuir-Blodgett (LB) technique, a monolayer on the water surface is transferred onto a substrate, which is raised and dipped through the surface. From this, multilayers can be obtained in which constituent molecules are periodically arranged. The LB technique has attracted considerable interest in the fabrication of electrical and electronic devices. Many researchers have investigated the electrical properties of monolayer and multiplayer films. Dendrimers represent a new class of synthetic macromolecules characterized by a regularly branched treelike structure. Multiple branching yields a large number of chain ends that distinguish dendrimers from conventional star-like polymers and microgels. The agobenzene dendrimer is one of the dendritic macromolecules that include the azo-group exhibiting a photochromic character. Due to the Presence of the charge transfer element of the azo-group and its rod-shaped structure, these compounds are expected to have potential interest in electronics and ptoelectronics, especially in nonlinear optics. In the present paper, we give pressure stimulation to organic thin films and detect the induced displacement current.